When I was testing the sentry command in the current version. My ships would only engage in battle, or fight back, when the enemy was in weapons range. I tried flipping them from Sentry to Defend Sector and their behavior seemed the same.
After engaging a target, they chased it, and did seem to run from the battle after about 2 sectors of chasing, like they should, but the ships didn't all stop chasing at the same moment though. The ship being shot at lingered for an extra minute, before retreating.
I hope both of these behaviors get improved upon. I thought about making phabricator bugs about them, but wasn't sure if I should, since fleets are still being worked on.